(1) Field of the Invention
The present invention relates to a display apparatus such as a plasma display. More particularly, the present invention relates to an image display apparatus for writing display information with reduced power consumption.
(2) Description of the Related Art
Typically, when a display apparatus such as a plasma display which displays images based on a two-value display method is used to display images, the display apparatus displays gray-scale images by dividing one field in the time domain into a plurality of sub-fields to which luminance weights are assigned, and controlling ON/OFF of light emission for each sub-field. For example, to display images with 256 gray-scale levels, one field is divided into 8 sub-fields, and assigns luminance weights “1”, “2”, “4”, “8”, “16”, “32”, “64”, and “128” to the 8 sub-fields in the order of time. The display apparatus receives an input digital signal that contains a set of 8 bits that correspond to the above sequence of sub-fields, in the reversed order of the bit sequence (i.e., the lowest bit corresponds to the lowest luminance weight).
FIG. 24 shows relationships between input gray-scale levels contained the input image signals and display gray-scale levels, and the luminance weights assigned to the sub-fields. FIG. 25 is a plot, based on the data shown in FIG. 24, of display gray-scale levels on the vertical axis vs. input gray-scale levels on the horizontal axis. The sub-field information shown in the drawings is written into display cells as the display information by applying voltage to the display cells via the address electrode.
The address electrodes have capacitances for other driving electrodes. Capacitances are also disposed between adjacent address electrodes. When the voltage waveform of the voltage applied to the address electrode changes greatly, a great amount of power is consumed for charging or discharging the capacitances. The amount of power consumed in the address driver also increases as the number of pixels to be displayed on the display apparatus increases, or as the driving voltage required for the addressing increases.
As a solution to the above problems, Japanese Laid-Open Patent Application No. 10-187093 discloses a technique that is equivalent to the one shown in FIG. 26. This technique intends to reduce the amount of power consumed in the address driver by shifting the timing of the driving waveform, removing the high-frequency component from the spatial frequency component of the input signal in accordance with the expected values of the amount of power consumed in the data driver, or omitting to display lower bits of the display signal in accordance with the expected values of power consumption amount.
Japanese Laid-Open Patent Application No. 2000-66638 (P2000-66638A) discloses a technique that intends to reduce the gray-scale levels of display images using a method in which data for sub-fields with smaller luminance weights is prevented from being written or changed, in accordance with the expected values of amount lost in the driver that are obtained from the display data changing patterns.
However, the conventional method of shifting the timing of the address driving waveform have a defect that it needs to secure a time for shifting the address driving waveform, and as a result, needs to lengthen the period of the address driving waveform. That is to say, the time required for the address driving over the whole period of one field is proportionate to the number of lines on the display apparatus. The time required for the address driving occupies relatively a large portion of the field, cycle. As a result, if the time required for the address driving increases slightly, the time that can be used for light emission greatly decreases. This makes it difficult to maintain the luminance.
The other method of restricting the number of display bits or display gray-scale levels in accordance with the expected values of power consumption amount also has a defect that to accurately expect the amount of heat generated in the driving device, it is required to add up a great amount of image information in the time and space domain. This increases the scale of circuits such as a memory device.
When, as is the case with the above conventional technique, the number of bits for the display image is changed only in accordance with the expected values of power consumption amount, the reduction of the number of bits or gray-scale levels may be noticed as image deterioration depending on the display images. This method also has a problem that a certain pattern in the whole image may be displayed as a different image depending on the position of the pattern in the whole image or depending on a combination with another pattern, or that an image that should move smoothly in time may move discontinuously. These phenomena allow viewers to feel unnaturalness.